Useful articles such as battery containers and battery container covers have in the past typically been molded from compositions comprising mixtures of rubber hydrocarbon polymer and a filler consisting of anthracite coal dust. A typical formulation of such a prior art composition is as follows:
Table A ______________________________________ (Prior Art) % by Weight ______________________________________ Rubber hydrocarbon polymer 9.021 Filler (anthracite coal dust) 74.399 Lime (activator) 4.903 Sulfur 2.287 Mold release agent 0.214 Accelerator 0.543 Oil 8.633 100.000 ______________________________________
It is noted that in the composition of Table A, the sulfur content is about 25.3% of the rubber hydrocarbon polymer content. The composition of Table A can be said to be a hard rubber molding composition, since the generally accepted definition of a hard rubber molding composition is one in which the sulfur-to-rubber hydrocarbon polymer ratio is greater than 25%.
The lime functions as an activator to activate the rubber for vulcanization. The sulfur functions as a vulcanizing (crosslinking) agent. The mold release agent can be a high molecular weight long chain aliphatic amine of the type offered for sale by Armour & Co. under the trademark ARMEEN. The accelerator can be of the aldehydeamine type, such as that available from Monsanto Company under the designation "A-100" , although other accelerators, such as diphenylguanidine (DPG), are equivalent to, and could be used in lieu of, A-100. The oil can be petroleum oil which acts as a plasticizer or softener. Other combinations of accelerators, activators and processing agents are also well known and can be used instead of the aforementioned agents to obtain desired cure rates.
It has heretofore been usual to determine whether or not a battery container or battery container cover is satisfactory by measuring hardness and impact strength. A minimum hardness of 63 Shore D has heretofore been considered necessary, in combination with an impact strength of at least 5 units, as defined hereinafter.
Anthracite coal dust is quite expensive. Consequently, many attempts have been made to substitute for anthracite coal dust lower cost filler materials, including specifically finely divided petroleum coke alone and in combination with strengthening agents such as Portland cement, as is suggested in Gentry et al. U.S. Pat. No. 2,883,358 which issued Apr. 21, 1959. Past efforts to substitute finely divided petroleum coke alone for anthracite coal dust have uniformly resulted in molded articles with such inferior physical properties that the articles were unsatisfactory.
More specifically, when finely divided petroleum coke was substituted for anthracite coal dust on a one-for-one basis and then molded under the conditions normally used for coal filled compositions, either the molded article was satisfactory as to flexural modulus but unsatisfactory as to impact strength, or else the material became completely degraded as the result of an overcure condition.